1. Field of the Invention
The present invention is generally directed to the field of semiconductor manufacturing, and, more particularly, to a method of controlling formation of metal layers.
2. Description of the Related Art
There is a constant drive within the semiconductor industry to increase the operating speed of integrated circuit devices, e.g., microprocessors, memory devices, and the like. This drive is fueled by consumer demands for computers and electronic devices that operate at increasingly greater speeds. This demand for increased speed has resulted in a continual reduction in the size of semiconductor devices, e.g., transistors. That is, many components of a typical field effect transistor (FET), e.g., channel length, junction depths, gate insulation thickness, and the like, are reduced. For example, all other things being equal, the smaller the channel length of the transistor, the faster the transistor will operate. Thus, there is a constant drive to reduce the size, or scale, of the components of a typical transistor to increase the overall speed of the transistor, as well as integrated circuit devices incorporating such transistors.
The manufacture of integrated circuit devices involves the formation of many layers of materials and, in some situations, the selective removal of portions of those layers using known photolithographic and etching processes. Such layers may be comprised of a variety of materials, e.g., metal, an insulating material, polysilicon, etc.
Sputter deposition, or physical vapor deposition (PVD), is widely used for forming thin layers of metals. Sputtering involves removing atoms from a solid material, or target, and then depositing the resultant vapor on a nearby substrate. Sputter deposition is usually performed in a diode plasma based system known as a magnetron sputtering tool. In this type of system, the cathode (or target) is sputtered by ion bombardment and emits metal atoms that are deposited on the wafer in the form of a thin film. Layers of metal may also be formed using chemical vapor deposition (xe2x80x9cCVDxe2x80x9d) processes.
As set forth above, magnetron sputtering tools are typically comprised of multiple chambers and a load/lock chamber for transferring wafers into and out of the various process chambers. The working chambers of such systems are manufactured from stainless steel, and the base pressure of such a system is generally below 10xe2x88x926-10xe2x88x928 Torr. Typically, the working pressure during sputtering is on the order of approximately 0.5-30 mTorr. Sputtering involves introducing a relatively high gas flow rate, e.g., 50-100 sccm of argon, nitrogen or xenon into a sputter deposition chamber to reach the sputtering working pressure. Magnetron sputter deposition systems are commercially available from a variety of vendors. For example, Novellus offers its Inova sputter deposition system and Applied Materials offers its Endura or Electra sputter deposition systems.
The deposited thickness of the metal film is typically controlled by controlling the duration of the deposition process. The deposition rate of the system is calibrated against time, and then a layer of metal is deposited for fixed time period. However, the thickness of the deposited layer is difficult to control for a variety of reasons, e.g., changes in sputter rate due to changes in target thickness, changes in the temperature of the system, and changes in pressure due to varying gas pumping rates. Moreover, such variations may occur from wafer-to-wafer (within run variations) and from lot-to-lot (run-to-run variations).
Test wafers are employed in attempts to monitor and control the thickness of deposited metal layers. More particularly, metal layers are deposited on such test wafers, and a variety of destructive and non-destructive metrology tests may be performed to determine the as-deposited thickness of the metal layer. For example, the test wafer may be cross-sectioned, and the thickness of the metal layer may be determined using a scanning electron microscope. Alternatively, the thickness of the metal layer may be determined using an elliposometer or an opto-acoustic method. However, these test wafers are relatively expensive, and thickness variations outside of acceptable limits may not be determined until well after additional wafers have been produced. As a result, the additional wafers may have to be scrapped if the deposition process is producing metal layers having a thickness outside of an acceptable range. Even if it is determined that the metal film on the product wafer had a thickness outside of an acceptable range, it is extremely difficult to change this thickness once the metal film is removed from the low-vacuum, low-pressure, multi-chamber environment of commonly employed deposition systems.
The present invention is directed to a method that may solve, or at least reduce, some or all of the aforementioned problems.
In general, the present invention is directed to methods of controlling the formation of metal layers. In one illustrative embodiment, the method comprises depositing a layer of metal above a structure, irradiating at least one area of the layer of metal, and analyzing the spectrum of x-rays leaving the irradiated area to determine a thickness of the layer of metal. In further embodiments of the present invention, the layer of metal may be comprised of titanium, cobalt, nickel, copper, molybdenum, etc. In yet further illustrative embodiments, a plurality of areas of the layer of metal are irradiated with x-rays.
In another illustrative embodiment, the method comprises depositing a first layer of metal above a structure, irradiating at least one area of the first layer of metal, analyzing an x-ray spectrum of x-rays leaving the irradiated area of the first layer of metal to determine a thickness of the first layer of metal, depositing a second layer of metal above the first layer of metal, irradiating at least one area of the second layer of metal, and analyzing an x-ray spectrum of x-rays leaving the irradiated area of the second layer of metal to determine a thickness of the second layer of metal.